• 대한수학회논문집
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• 제30권4호
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• pp.429-438
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• 2015

In this paper, we discuss how the operational calculus can be exploited to the theory of mixed generating functions. We use operational methods associated with multi-variable Hermite polynomials, Laguerre polynomials and Bessels functions to drive identities useful in electromagnetism, fluid mechanics etc. Certain special cases giving bilateral generating relations related to these special functions are also discussed.

• International Journal of Ocean System Engineering
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• 제3권1호
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• pp.22-32
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• 2013

A heuristic physical theory of diffraction (PTD) for an acoustic impedance wedge is proposed. This method is based on Ufimtsev's three-dimensional PTD, which is derived for an acoustic soft or hard wedge. We modify the original PTD according to the process of physical optics (or the Kirchhoff approximation) to obtain a 3D heuristic diffraction model for an impedance wedge. In principle, our result is equivalent to Luebbers' model presented in electromagnetism. Moreover, our approach provides a useful insight into the theoretical basis of the existing heuristic diffraction methods. The derived heuristic PTD is applied to an arbitrary impedance polygon, and a simple PTD formula is derived as a supplement to the physical optics formula.

• Journal of Astronomy and Space Sciences
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• 제32권2호
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• pp.151-159
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• 2015

The fundamental conception in physics of the propagation of the electromagnetic wave polarization in matter is newly understood as the cardinal keyword in free-space quantum communication technology and cosmology in astrophysics. Interactive visualization of the propagation mechanism of polarized electromagnetism in a medium with its helicity has accordingly received attention from scientists exploiting the protocol of quantum key distribution (QKD) to guarantee unconditional security in cryptography communication. We have provided a dynamic polarization platform for presenting the polarization modes of a transverse electromagnetic wave, converting the state of polarization through the arrangement of optical elements, using Jones vectors calculations in Methematica. The platform graphically simulates the mechanism of production and propagation of the polarized waves in a medium while satisfying Maxwell's equations.

• 대한전기학회논문지
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• 제43권2호
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• pp.268-277
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• 1994

Current sensor using Hall device is an instrument of detecting a current by Hall effect. The existing current sensor is ordinarily worked by concentrating electromagnetism produced around the conducting wire turned iron core. The tiny curren, however, could not be accurately detected by the instrument owing to influence of residual magnetism exisisting in iron core, and the result of detecting is also somewhat on the large side. kAccordingly, We fabricated a new type of instrument minimizing the influence of residual magnetism existing in iron core and detected the tiny DC current accurately by taking advantage of magnetic modulation. The range of measuring DC current is 0[mA]-100[mA] and the maxiumm Linerity tolleance by the result of detecting current, can be reduced less than 3 percent.

• ETRI Journal
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• 제31권1호
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• pp.77-79
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• 2009

The wave concept iterative procedure (WCIP) is used to analyze a quasi-square open metallic ring frequency selective surface (FSS). The quasi-square open metallic ring FSS is dual-polarized. When the incident plane wave is polarized in a direction parallel to the FSS' coupled parallel strips, it shows two rejecting bands. Moreover, another rejecting band can be obtained if the source plane wave is perpendicularly polarized with respect to the FSS' coupled parallel strips. The three resonant frequencies are inversely proportional to the length of the FSS' coupled strips to provide an easy fine tuning of the FSS structure. The simulated results obtained using WCIP are compared to the measured results, and a good agreement is reported.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제40회 동계학술대회 초록집
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• pp.11-11
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• 2011

In this talk, I will discuss roles of pseudo vector and scalar potential in changing physical properties of graphene systems. First, graphene under small uniaxial strain is shown to be described by the generalized Weyl's Hamiltonian with inclusion of pseudo vector and scalar potential simultaneously [1]. Thus, strained graphene is predicted to exhibit velocity anisotropy as well as work function enhancement without any gap. Second, if homogeneous strains with different strengths are applied to each layer of bilayer graphene, transverse electric fields across the two layers can be generated without any external electronic sources, thereby opening an energy gap [2]. This phenomenon is made possible by generation of inequivalent pseudo scalar potentials in the two graphene layers. Third, when very tiny lateral interlayer shift occurs in bilayer graphene, the Fermi surfaces of the system are shown to undergo Lifshitz transition [3]. We will show that this unexpected hypersensitive electronic topological transition is caused by a unique interplay between the effective non-Abelian vector potential generated by sliding motions and Berry's phases associated with massless Dirac electrons.

• 대한수학회보
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• 제24권1호
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• pp.31-37
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• 1987

I want to focus on developments in the areas of general relativity and gauge theory. The topics to be considered are the singularity theorms of Hawking and Penrose, the positivity of mass, instantons on the four-dimensional sphere, and the string picture of quantum gravity. I should mention that I will not have time do discuss either classical mechanics or symplectic structures. This is especially unfortunate, because one of the roots of differential geometry is planted firmly in mechanics, Cf. [GS]. The French geometer Elie Cartan first formulated his invariant approach to geometry in a series of papers on affine connections and general relativity, Cf. [C]. Cartan was trying to recast the Newtonian theory of gravity in the same framework as Einstein's theory. From the historical perspective it is significant that Cartan found relativity a convenient framework for his ideas. As about the same time Hermann Weyl in troduced the idea of gauge theory into geometry for purposes much different than those for which it would ultimately prove successful, Cf. [W]. Weyl wanted to unify gravity with electromagnetism and though that a conformal structure would fulfill thel task but Einstein rebutted this approach.

• 한국과학교육학회지
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• 제28권7호
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• pp.730-748
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• 2008

Students often have tenacious physics misconceptions and many studies were conducted on engendering conceptual change. Correspondingly, there is much literature on alternative assessment and its role in student learning. This is a comparison study on using alternative assessments to improve common students' misconceptions in GCE Advanced Level Physics. This research also aims to affirm alternative assessment as a valid tool for learning and promote its use. This study involved two classes with 24 students each. For four weeks, electromagnetism was taught to students using the same classroom pedagogies but with different assignments. The control group completeda standard drill-and-practice assignment while the experimental group finished an alternative assessment. From the preliminary results, students who undertook the alternative assessment and the traditional assessment both improved, however, the treatment group did not perform statistically significantly better than the control group. The reasons will be discussed and commented and it is expected to have significant improvement on rectifying misconceptionsupon next batch of experimentation groups.

• 한국초등과학교육학회지:초등과학교육
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• 제25권spc5호
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• pp.476-484
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• 2007

본 연구의 목적은 일반 학생과 과학 영재 학생들의 열, 전자기, 힘, 빛 개념을 중심으로 한 물리 영역에 대한 오개념을 조사하여, 과학 영재 학생과 일반 학생을 비교하여 개념의 이해도, 오개념의 유형에 어떤 차이가 있는지 알아보기 위한 것이었다. 연구 대상은 대구 지역의 영재교육원의 과학 영재 75명과 동일 지역에 소재하고 있는 두 개의 초등학교 5, 6학년 학생 148명을 표집했다. 선행 연구와 교육 과정 분석을 통해 물리 영역에 대한 초등학교에서 갖추어야 할 개념을 선정한 후, 기존의 물리영역에 대한 개념 검사 도구를 보완 및 수정하여 문항을 작성하였으며, 일부는 개발하여 선택형과 진술형으로 초등학교 물리 오개념 검사 도구를 개발하였다. 20문항으로 구성된 그 검사 도구는 열개념, 전자기 개념, 힘 개념, 빛 개념을 대상으로 하며 각 개념별로 5가지의 하위 개념을 조사하였다. 진술형 문항에 의한 결과를 바탕으로 과학 영재학생과 일반 학생의 물리 개념의 이해도 차이를 분석하였고, 선택형 문항에 의한 결과를 바탕으로 오개념의 차이를 분석하였다. 연구 결과로 첫째, 열 개념, 전자기 개념, 힘 개념, 빛 개념에서 과학 영재 학생과 일반 학생 모두 이해도가 비교적 낮았으나, 과학 영재 학생이 일반학생보다 모든 물리 영역에서 개념 이해도가 통계적으로 유의하게 높은 것으로 나타났으며, 이로부터 과학 영재 학생이 일반 학생에 비해 물리 영역에 대한 개념에 대한 이해 수준이 높았다고 말할 수 있다. 또 과학 영재 학생이나 일반 학생 모두 개념 이해도가 전자기 개념, 열 개념, 힘 개념, 빛 개념 순으로 낮아져서 과학 영재 학생이나 일반 학생이 각각서로 다른 어떤 특정 개념의 이해에 곤란을 겪는 것은 아니고, 동일 개념에 대해 비슷한 난이도를 느끼고 있음을 보여주었다. 둘째, 과학 영재 학생과 일반 학생은 대부분 비슷한 오개념 유형을 나타냈으며 과학 영재 학생은 일반 학생에 비해 오개념을 적게 가지고 있었다. 결론적으로 초등학교 과학 영재 학생도 일반 학생처럼 과학에 대한 오개념을 가지고 있지만, 오개념이 정착되지 않아 학습 후 과학적 개념으로 쉽게 수정될 수 있는 가능성을 보여주었다.

• 한국초등과학교육학회지:초등과학교육
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• 제26권4호
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• pp.440-448
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• 2007

The purpose of this study is to examine elementary students' conceptions of magnetic fields around various magnets by drawing tasks. A total of 105 elementary students from the 3rd and 6th grade levels were asked to draw how iron filings would arrange around magnets. We classified their drawings of magnetic field lines with some criteria to identify conceptions of magnetic forces and checked them through interviewing about their representative drawing. Through analyzing drawings, we discovered that 40% of elementary students drew the correct arrangement of iron filings around a bar magnet. In the case of two bar magnets in opposite directions, 33% of them drew correct patterns of iron dust and around two magnets in the same direction only 20% did well. Only 2.9% and 7.6% of students presented the correct drawings of magnetic fields near a disc and a horseshoe magnet. While 3rd grade students were supposed to be poor in drawings of magnetic fields around a loose and a dense coil which was not learned about, only 31% and 23% of 6th grade students who have just studied electromagnetism properly drew patterns of iron dust. This shows that only one quarter of students understood the magnetic filed lines even after instruction of electromagnetism. Many of 6th grade students learned a solenoid becomes just as a permanent magnet, but very few of them correctly drew a magnetic field line could distinguish between the iron dust around a loose and dense coil. After interviewing students, it is found that students consider magnetic forces to be existed only in parts of magnet because many of them drew magnetic field line of a specific areas around magnets. Students had misconceptions that magnetic forces exist only on the poles not in the middle around a horseshoe magnet. Also the disc-shape magnet made students to reveal various types of misconceptions: N- and S-poles are mixed in a whole magnet and right part of a disc-shape magnet is N-pole, left part is S-pole. Students who had not studied magnetic fields of around a magnet and electromagnets could not draw the correct patterns of iron dust suggest that it is indispensable for students to teach how patterns of iron filings would represent a visual image of magnetic fields in order to understand magnetic fields.